1. Field of the Invention
This invention relates to a high frequency heating apparatus, such as a microwave oven, and, more particularly, to an attachment structure of a mounting rack thereof.
2. Description of the Related Art
Conventionally, a microwave oven range includes a mounting rack (hereinafter referred to as a shelf) situated at a lower portion of a housing, and on which is placed food or the like for heating, and a radiating unit, mounted on an upper portion of the housing, and which radiates microwaves downward, onto food placed on the shelf. However, because of the distance between the shelf and the radiating unit, food or the like placed on the shelf cannot always be heated uniformly.
In the conventional microwave oven, in order to uniformly heat an object to be heated, the following structure has been considered to make the distance between the microwave radiating unit and the shelf as short as possible.
More specifically, the conventional microwave oven range includes an excitation port of a waveguide serving as a microwave radiating unit and a stirrer fan in a bottom portion of a heating chamber. In the microwave oven of this type, the heating chamber is partitioned into upper and lower spaces by a food mounting shelf. The stirrer fan is arranged in the lower space partitioned by the shelf.
The shelf for supporting food is generally a flat one-piece member. Therefore, when liquid food is spilled, the spilled food may undesirably fall into the lower stirrer fan chamber through a gap between the shelf and a wall surface of the heating chamber.
In the conventional manner of solving the above problem, as shown in FIG. 10, a shelf 1 is mounted in a heating chamber 2, and a gap between the peripheral edge of the shelf 1 and a wall surface 3 of the heating chamber 2 is filled with a silicone material 4 to perform sealing. However, when this sealing system is employed, a syringe is inserted in the small heating chamber 2, and the silicone material must be injected with a visual observation along the gap. This operation is time-consuming and it is difficult to inject a uniform amount of silicone material, thus degrading operation efficiency. In addition, when a stirrer fan 5 or the like arranged in a lower space of the shelf 1 fails, the shelf 1 must be detached during maintenance service. The silicone material 4 filled in the gap cannot be easily detached, thus making it difficult to detach the shelf 1. In the worst case, parts cannot be replaced without damaging the shelf 1 or a main body 6.
As disclosed in Japanese Patent Disclosure (Kokai) No. 62-218736 (FIGS. 11 and 12), a packing 7 is mounted at a peripheral edge of a shelf 1, and the shelf 1 is fitted in a heating chamber 2 from above, so that the gap between the peripheral edge of the shelf 1 and a wall surface 3 of the heating chamber 2 is sealed by the packing 7. When routine maintenance is to be performed on this microwave oven, an upper portion of the packing 7 mounted at the peripheral edge of the shelf 1 is pressed by a finger and elastically deformed, making it easy to detach from the shelf 1, which in turn can then be easily detached.
However, since a contact surface 8 between the end face of the shelf 1 and the packing 7 is formed to be perpendicular to the surface of the shelf 1, the packing 7 is urged between the shelf 1 and the wall surface 3 of the heating chamber 2 and deformed in the X direction, as shown in FIG. 11, when the shelf 1 in the heating chamber 2 is pressed from above. As shown in FIG. 12, when the shelf 1 is pushed downward, the packing 7 becomes detached from the shelf 1, thus degrading the sealing of the shelf 1.
As described above, when the gap between the peripheral edge of the shelf 1 and the wall surface 3 of the heating chamber 2 is filled with the silicone material 4, the silicone material 4 cannot be easily detached during maintenance service. Therefore, it is difficult to easily detach the shelf 1. In order to improve the serviceability, the packing 7 may be mounted at the peripheral portion of the shelf 1 to achieve easy detachment of the packing 7. However, as described above, when this system is employed, the packing 7 is apt to be detached upon assembly.